Electrification from the Rails
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Although a critical factor in overall model performance, this subject has typically been given little attention when evaluating models and their performance. It has been a common practice among many importers/builders to single insulate O scale models, which means that the chassis/frame and/or trucks are used as electrical 'conductors' with the wheels on only one side of the model insulated from the chassis/frame. Unless the electric potential is drawn directly from the axles on the un-insulated side of the model, other factors such as axle bearing material, ball-bearing (if used) classification and types of lubricant must be evaluated since they will be conductors in the potential's path. On models with open clearance and minimal detailing adjacent to drivers and wheelsets, where shorting can be a problem and that do not have sound and/or DCC (Digital Command Control) installed, single insulation can be an acceptable choice.
With the advent of sophisticated sound and Digital Command Control systems, the quality of delivered electrical potential has become ever more important. All Kohs & Company driver and wheel sets are double insulated, meaning that every driver tread or wheel is electrically insulated from the axle to which it is attached. Using double insulation serves multiple purposes: our locomotive chassis/frames and trucks operate in a electrically neutral state which minimizes the potential shorting of close-tolerance components and also reduces the number of moving parts in the current carrying and grounding paths which reduces the induced electronic 'noise'. By using spring loaded plungers fabricated from non-arcing conductive material running against the backside of each driver, we are assured of the most positive contact possible in transferring the electric potential from the rail to the internal wiring of our models. By drawing current from only the drive wheels of the model, which carry the majority of the model weight, we minimize the potential for arcing between the treads and railheads. Drawing electric potential from un-weighted wheels, which often have intermittent contact with the railheads, can create arcing and induce electronic 'noise' in the system. Although more expensive and time consuming in assembly, the double insulated approach combined with the correct selection and application of materials provides the most consistent and predictable performance possible.
The National Model Railroad Association 'Recommended Practices', RP-9, Section III B provides the following guidance on this subject: "A low resistance connection shall be provided from motor terminals to the wheels without relying on axle to side frame contact, or truck bolster to body bolster contact, or drawbar to pin contact".
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